The invention relates to drilling methods useful in the oil and gas industry. In particular, materials and methods for chemically enhanced drilling are disclosed.
Both drilling and/or jetting holes in rock are practiced in several industries, including the oil and gas industry as well as the underground pipe and cable laying industry. Drilling is normally accomplished by the use of rotary or percussion bits, aided by fluid jets designed to sweep the cut rock away from the cutters. In some instances the power of the jets may also be used to enhance the cutting efficiency of the bit. Drilling specifically by jetting is normally accomplished by using high velocity jets, usually with water, to mechanically erode the surface of the rock. Such jetting drilling is typically limited to softer, weaker formations, normally found at shallower depths.
Stimulation of a drilled well is often required. Acid is commonly used in the oil and gas industry to stimulate wells and to increase the production rate of the treated wells. The acid works in at least one of four ways: (1) by increasing the permeability of the rock around the well bore; (2) by creating wormholes extending out from the well bore (small random tunnels created in the formation); (3) by removing matter introduced into the formation by the drilling process such as polymers or particles of calcium carbonate; and (4) by fracturing the formation and then dissolving material away from the fracture to create production planes so that a high conductivity site is created.
The use of continuous reeled tubing (xe2x80x9ccoiled tubingxe2x80x9d) has been limited to a small percentage of wells due to its high equipment and personnel costs, low rates of penetration, and issues related to the reliability of high-cost xe2x80x9csmartxe2x80x9d bottom hole assemblies needed for directional drilling. This is despite significant improvements in the quality and dimensions of coiled tubing itselfxe2x80x94pipe sizes have increased from 1 inch OD to 3.5 inch OD and greater.
Conventional drilling and jetting methods have several significant shortcomings. The drilling methods produce large amounts of rock cuttings which must be brought to the surface in order to create the well. The transport of the cuttings requires the use of special drilling fluids capable of suspending the cuttings. Handling equipment is required at the site surface to handle, store, and dispose of the cuttings. The drilling fluids are often separated from the cuttings and recycled, all of which requires considerable effort, time, and expense. Conventional drilling machinery is mechanically complicated, expensive, and contains multiple parts that may be subject to failure or wear.
Thus, there exists a need for improved drilling methods that are effective and maximize production while minimizing expense.
Acids and other chemicals have been used to increase the permability of the rock remaining around a main borehole constructed by mechanical means. These chemicals have not been used as the primary method of constructing the well bore. This is despite a multitude of ideas been tried using different rotary devices, percussion devices and mechanical jetting devices.
Hole construction using a dissolving fluid alone, or a dissolving fluid with conventional mechanical methods does not fit well with conventional drilling practices and equipment. Conventional drilling practices require that the wellbore constructed be xe2x80x9csealedxe2x80x9d as it is drilled to maintain xe2x80x9ccontrolxe2x80x9d of the hole. The chemically enhanced drilling method described herein does not provide for this. Also, conventional drilling rigs are not well suited to handling corrosive fluids. Hence chemically enhanced drilling methods have not been previously developed.
Several changes in the industry are the growing acceptance of underbalanced drilling as a method of constructing holes without xe2x80x9csealingxe2x80x9d them, and the growing acceptance of using coiled tubing to drill holes. Continuous reeled tubing (xe2x80x9ccoiled tubingxe2x80x9d) operations are ideally suited to using corrosive fluids. There now exists methodology and apparatus to permit an old method of pumping acid to be used for the new application of creating wellbores.